[R] nearest neighbour interpolation
B.Rowlingson at lancaster.ac.uk
Fri Jan 31 13:38:02 CET 2003
Roger Bivand wrote:
> Point-in-polygon functions are in the splancs
> package, but there you need the polygons.
There's also nearest-neighbour functions in Splancs - the nn2d
function returns the distances and indices of the nearest points in one
set (the grid) to another set (the data points). 'Interpolation' is then
just a matter of taking the value of the factor indexed by the result.
Its easier to do than describe.
It is inefficient though, since it computes all Npts x Ngrid neighbour
distances. Horrible if you want to do a large number of simulations, but
if it takes twenty minutes and you only have to do it once, put the
kettle on and have a cup of tea while the Computer Scientists tell you
how to improve the algorithm. The function will be finished and your tea
drunk by the time they've explained it.
> There are functions in package spatstat too, for instance
> nearest.raster.point() does the reverse of what you want - which raster
> cells are nearest to point coordinates - not which are closer.
Hopefully Rasp will have better point/polygon/nearest-neighbour
> Please contact me off-list if I can help further.
I've emailed Matt the splancs-based solution.
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